Method of applying protective layers on metals or other electric conductors



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' Hl-TD JONA HJALMAE MELLQlIItET, Q13 STOCKHQL'M, SWEDEN. METHOD OFAPPLYING PEOTEGTXVE LAYERS N METALS OR OTHER ELECTRIC CONDUCTORS.

No Drawing, Application filed August 1, 1924, Serial No. 725,656, and inSweden'August 23, 1823.

lt is known that iron is rendered passive The bath to be electrolizedmay 'bepre by being used as-an anode in an alkaline pared as follows:solution a ndthat this quality is highly inr A solution of a lead salt,such as lead 55 creased by precipitating on the iron a layer acetate ornitrate, is added with a solution of high oxidation potential, such aslead of a tartrate of an alkali metal, such as peroxide. Attempts havebeen 'made to sodium-potassium tartrate. The precipitautilize thiscondition for technical purposes tion thus formed, which in a dry stateis a in order to protect the iron against rusting. white finecrystalline powder, correspond- 60 If a solutionot, for instance, leadnitrate ing to the empiric formula PoTa, is washed 19 be electrolyzed,there is form-ed on the anode by repeated decantations and is finallysusa layer of lead peroxide but after a relapended in water, whereupon asolution of tively short period such a bath will be acidiabout of analkali such as NaOH or tied by the liberated nitric acid which ammoniais added in slight excess until a 65 attacks the objects used as theanode and is clear solution is formed. A complex alkaligradually reducedto nitrous acid so that lead compound of tartaric acid is therebyfinally no further precipitation of peroxide formed. occurs. i lnothe'rmethod of qbtaining such av solu- By using as an electrolyte a solutiontion which can be more easily executed con- 7 obtained by boiling leadoxide in a concensists in. shaking a solution ofa tartrate of 2Q tratedalkali solution great inconveniences an alkali metal to which has beenadded a soon occur which make the process inappli suitable quantity offinely pulverized lead cable for technical use, such inconveniencesoxide or leadhydrate. If for instance a principally consisting in thisthat the tens solution containing 50 grams of sodiumsion will be exposedto strong variations an. potassium tartrate per litre is shaken toeevolution of gases occurs and a slimy mixgether with a suitable quantityof finely ture of hydrates of lead of difierentstages pulverized leadoxide an alkaline solution of oxidation is formed. i is obtained whichcontains about grams It has now been discovered that such of lead insolution per litre. The dissolvw layers of a high oxidation potentialmay be ing takes place more rapidly if at the beginprecipitated on theanodes very easily withning alkali is added and the mixture foutanydisturbing actions or variations of heated. The obtaining of acorresponding the tensions by using as an electrolyte an solution ofmanganese is more diflicult, and,

alkaline solution of a lead man anese or. moreover such a solution has atendenc of other metal salt of a hydroxy carboxylic being ()KrllZfid bythe air.

35 acid, which metal is adapted to form For technical purposes the'bathQniay be peroxides. Amongst such acids the tartaric produced in thefollowing manner, the quanacid is preferred due to its relati ely lowtitres of the ingredientsaswell as'tllemethod price. p itseli being onlygiven as examples: W

The present invention therefore has for its F E I object to provide anelectrogalyanic method v 3 6 of applying protective layers to electriccon- 150 grams of pure sodium hydrate are ductors especially metals,which. consists in dissolved in 10- litres of distilled water, usingsaid conductors an anode inan allra whereupon alter stirring grams of o-95 line solution, including animonical hydroxy tassiuin hitartrate areadded. When t is carhoxylic acid of a salt of a metal adapted salt beendissolved fill lidtl grams of to form peroxide. Tlhe preferred saltsused finely pulverized lead oxide added and in carrying the inventioninto practice are the mixture stirred. Together with said lead ormanganese salts oi hydroxy caroxide one may add manganese oxide ormanboxylic acids, especially of tartaric acid, but ganese hydrate. Themixture is then vigoralso such salts oi": other metals adapted to; ouslystirred from time to time while being form peroxides may be used. suchas nickel heated it desired, until most of the lead has cobalt hit-smithdissolved. After the undissol ed residue before being placed into thebath.

has settled to the bottom the Example I].

The bath may be composed as follows:

' 10 litres of water, 500 grams of sodiumpotassium tartrate, -100 gramsof sodium hydrate, 400-500 grams of finely pulverized lead oxide.

On executing the methpd one may-use as a cathode plates of iron or othersuitable metal of convenient shape and size and as an anode the objectson which the protective layer is to be precipitated. The objects used asthe anode are freed from fat and carefully purified in any convenient mannler i t 1e anode consists of iron it may be conveniently treated witha 10% solution of nitric acid and the remaining carbon may be removed bybrushing or in any other convenient manner. The objects may also bepurified by subjecting them to the action of sand blast in which casethe surface will be more smooth than by using chemical agents. Generallythe result will be best if the anodeobjects are made matte in some Wayor other.

When the layer has received the desired thickness the objects'arerapidly removed from the bath, flushed with a stream of water whichshould first be cold and then hot, and finally they are dried. Bysuitably'adapting the length of the period during which the objects areexposed to the galvanic action a perfectly even and rigidly adheringlayer or cover is obtained on'the objects used as the anode. Said layerhas -a dark-blue or dark-gray colour and consists of hydratic peroxideof lead or manganese.

The above described method which is Well adapted for working on atechnical scale makes it possible to a ply on objects of iron or othermetals or ot 1er electric conductors, such as carbon, a protective layeror cover which will protect the objects against the corrosive action ofthe atmosphere, of acids, gases and other agents. Objects of iron, forinstance, will in this manner be protected against rusting. The layer orcover thus obtained will obtain a deep black colour if the objects areprovided with a cover of pyroxyline varnish or dipped into a solution ofparafiin, Wax 0r similar substances. For obtaining covers of greaterthickness, for instance on objects adapted to be used as or inconnection with electrodes a considerably longer period is of courserequired than in case of producing a cover protecting against rust.

lVhenever the process is interrupted, for instance at the end of a daythe undissolved lead oxide on the bottom of the vessel is stirred in theliquid until the latter contains the original amount of lead insolution. Fresh oxide of lead is introduced into the liquid only whenthe undissolved quantity on the bottom of the vessel has been consumed.

I claim:

1. Electrogalvanic method of applying a protective layer of highoxidation potential on electric conductors, especially materials,consisting in using said conductors as an anode inan alkaline solutionof an oxi carbonic acid salt of a metal adapted to form peroxides.

2. Electrogalvanic method of applying protective covers on electricconductors especially metals, consisting in using said conductors as ananode in an alkaline solution of a lead salt of a hydroxy carboxylicacid.

3. Electrogalvanic method of applying protective covers on electricconductors especially metals, consisting in using said conductors asanode in an alkaline solution of a lead salt of tartaric acid.

4. Electrogalvanic method of applying protective covers on electricconductors especially metals consisting in using said conductors as ananode in an alkaline solution of a lead salt of an oxi carbonic acid andin subjecting the same to a bath consisting of a solution of a leadcompoundin an alkaline tartaric solution. a

5. Electrolytic bath adapted to be used in executing the method setforth in claim 2. consisting of a solution of a lead compound in alkalitartrate solution to which has been added an alkali.

6. Electrolytic bath adapted to be used in executing the method setforth in claim 2, consisting of a solution of a mixture of a leadcompound and a manganese compound in an alkali tartrate solution.

In testimony whereof I have affixed my signature.

J ONAS HJALMAR METJLQUIST.

